Cells are continually challenged on a daily basis, resulting in multiple lesions forming in DNA. The lesions, if not repaired, can lead to mutations or cell death, thus complex signalling networks exist which ensure that lesions are detected and repaired to maintain the integrity of DNA.
Detection of DNA damage initiates a series of events which are key in maintaining the genome. Cell cycle checkpoints are designed to stop the cell cycle and allow repair of the lesion before allowing the cell to continue into mitosis.
Two key checkpoints have been identified, one at the end of the G1 phase and the second at G2, working in tandem to ensure all lesions are identified and repaired. In 50% of human cancers the G1 checkpoint is non-functional due to mutations in the tumour suppressor gene p53. However, the G2 check-point is seldomly mutated and often found to be activated in cancer cells. Cancer cells exploit this to confer resistance to treatment modalities, including DNA damaging agents and radiation.
Three kinases have been identified as key regulators of the G2 checkpoint, namely Chk1, Chk2 and Wee-1. Inhibitors for these kinases are currently being evaluated in clinical trials.
Wee-1 is a nuclear tyrosine kinase which negatively regulates entry into mitosis at the G2/M check-point by catalysing a phosphorylation of the cdc2/cyclin B kinase complex. The phosphorylation occurs on the tyrosine-15 residue and leads to the inactivation of the cdc2/cyclin B complex, ultimately preventing mitosis. Wee-1 function is intimately linked to that of Chk1 and Chk2 due to their phosphorylation and inactivation of cdc25 on serine-216, as well as the reported activation of Wee-1 by Chk 1 & 2 (Ashwell et al., 2012, DNA Repair in Cancer Therapy, DOI: 10.1016/B978-0-12-384999-1.10010-1).
Wee-1 is downstream of the Chk family and is a crucial component of the checkpoint signalling cascade as it prevents cells from entering mitosis if lesions are detected (Do et al., Cell Cycle 2013 12 (19) 3159-3164).
Commonly administered anti-cancer compounds induce DNA damage, including antimetabolites, platinum agents, topoisomerase inhibitors and alkylating agents. However, their efficacy is limited due to excessive toxicity, resistance and lack of tumour selectivity. Compounds which work in combination with these agents to prevent DNA repair selectively in tumour cells would be extremely beneficial. As the tumour suppressor gene p53 is commonly mutated in tumour cell lines, the administration of a Wee-1 kinase inhibitor, abrogating the G2 check point, may lead to increased sensitivity to DNA damaging agents. The potential for this has been reported, as silencing of Wee-1 activity was sufficient to sensitize HeLa cells to doxorubicin due to abrogation of G2 arrest. By contrast, in normal breast epithelium due to the fully competent p53 protein, the removal of Wee-1 function had little additional effect compared to doxorubicin alone (Wang et al., 2004, Cancer Biology and Therapy, 3(3), 305-313).
It has been reported that cell lines harbouring mutations in the tumour suppressor gene p53 had increased sensitivity to DNA damaging agents when co-administered with Wee-1 small molecule inhibitors. Synergistic in vitro and in vivo efficacy has been reported when small molecule inhibitors were combined with gemcitabine, 5-fluorouracil, carboplatin, cisplatin (Hirai et al 2010, Cancer Biology & Therapy 9:7, 514-522), cytarabine (Tibes et al., 2012, Blood, 119(12), 2863-2872), for example. Other examples of chemosensitization upon Wee-1 inhibition include but are not limited to combination with irinotecan, topotecan or alkylating agent (temozolomide). Radiosensitization has also been demonstrated in multiple cancer types (Havelek R., et al. 2014 Biochem Biophys Res Commun., 24 (453), 569-75; Caretti V., et al. 2013 Mol Cancer Ther., 12 (2) 141-50; Bridges K A., et al. 2011 Clin Cancer Res., 1(17), 5638-48; PosthumaDeBoer J., et al. 2011 BMC Cancer., 29 (11), 156). Combinations with non-cytotoxic compounds have also been evidenced including for instance with Chk-1 inhibitors (Carrasa et al., 2012 Cell Cycle 1:11(13):2507-2517), (Russell et al., 2013 Cancer Res. 15; 73 (2) 776-784), Src inhibitors (Cozzi et al., 2012, Cell Cycle 11(5), 1-11), PARP inhibitor (Karnak D., et al. 2014 Clin. Cancer Res., 1 (20), 5085-96), HSP90 inhibitor (Lokeshwar V B., 2012 Cell Cycle., 15 (11), 3722-3; Iwai A., et al. 2012 Cell Cycle 1 (11), 3649-55), HDAC inhibitor (Zhou L., et al. 2015 Leukemia, 29(4), 807-18). Interestingly, single agent apoptotic efficacy, independent of p53 status, has also been reported in various cellular models and contexts including sarcoma cell lines and in patient-derived sarcoma samples (Kreahling et al., 2012, Mol. Cancer Ther., 11(1), 174-182) in a panel of cancer cell lines in vivo including lung and melanoma model cell lines (Guertin et al., 2013 Mol Cancer Ther, 12 (2) 141-151) or more recently in H3K36me3-deficient cancer cell lines (Pfister S X., 2015 Cancer Cell., 28(5), 557-568).
Irradiation is known to increase phosphorylation of the Tyr15 and Thr14 residues of cdc2, leading to a radioresistant phenotype. Inhibition of Wee-1 activity by small molecule inhibitors (Wang et al., 2004, Cancer Biology and Therapy 3(3), 305-313), (Caretti et al., 2013 Mol Cancer Ther. 12 (2) 141-150) leads to a reduction in phosphorylation and radiosensitization, with the effect being more pronounced in p53 mutant cell lines.
It has been reported in melanoma that over-expression of Wee-1 is correlated with poor clinical outcome (Magnusson et al., 2012 PLoS One 7; (6)e38254), indicating it may have a significant role as a biomarker and as a targeted therapy.
Compounds having a kinase inhibitory effect, for example a Wee-1 kinase inhibitory effect, are described in WO2007/126122, US2010/0063024, EP 2,213,673, WO2008/133866, US2007/0254892, WO2012/161812, WO2013/126656, US2013/0102590, WO2013/059485 and WO2013/013031.
WO2007/126122 and US2007/0254892 describe various dihydropyrazolopyrimidinone derivatives as having a kinase inhibitory effect.
It is one object of the present invention to overcome at least some of the disadvantages of the prior art or to provide a commercially useful alternative thereto.
It is a further object of the present invention to provide a compound having an enhanced or comparable Wee-1-kinase-inhibitory effect compared to known compounds or compositions.
It is a further object of the present invention to provide compounds having an improved or comparable potency in cells compared to known compounds or compositions.
It is a further object of the present invention to provide compounds with an improved or comparable selectivity towards Wee-1 kinase compared to known compounds or compositions.
It is a further object of the present invention to provide a compound having an improved efficacy and tolerability when administered in combination with other therapies compared to known compounds or compositions.